Photolithography has been a standard method of printed circuit board (PCB) and microprocessor fabrication. The process uses light to make the conductive paths of a PCB layer and the paths and electronic components in a silicon wafer of microprocessors.
The photolithography process involves light exposure through a mask to project the image of a circuit, similar to a negative image in standard photography. This process hardens a photo-resistive layer on the PCB or wafer. The hardened areas stay behind in the form of circuit paths of printed circuit boards (PCBs) and central processing units (CPUs). Unexposed areas are then dissolved away by a solution bath, such as an acid in wet methods or plasma-like oxygen ions in dry methods. A PCB might have as many as twelve or more of these layers and a processor may reach upwards of thirty or more, with some comprising metallic conductive layers and others insulating layers. Other steps include deposition of conductive metallic elements.
Process shrinks, also known as die shrinks, are one of the main ways that the miniaturization of electronic devices is made possible. Photolithography process shrinks involve miniaturization of all semiconductor devices, particularly transistors. Processors made on a smaller scale generally mean more CPUs per wafer, either for cheaper production or a more complex and powerful processor in a given die size. Progress in miniaturization also fosters faster transistor switching speeds and lower power consumption, so long as there is not too much current leakage (which is one of the challenges that increase with this progress).
Photolithography is the selective removal of the oxide in a desired area of a substrate. Thus, the areas over which diffusions are effective are defined by the oxide layer with windows cut in it, through which diffusion can take place. The windows are produced by the photolithographic process. This process is the means by which microscopically small electronic circuits and devices can be produced on silicon wafers resulting in billions of transistors on a 1 cm by 1 cm chip.
However, partly due to its lack of a high-temperature fusing process such as sintering, photolithography has had very limited value in integrating relatively large capacitors, inductors, and resistors (“passive” components), forcing the continued use of discrete components. Manufacturing with discrete components is inherently more expensive, bulky, and wasteful of material than an integrated approach. Instead of trying to mount the larger components, onto a chip, or create them with photolithography, a more efficient and effective system and method of integration is required.